Laser demos silicon-opto convergence

Portland, Ore.  Intel Corp. claims to have developed the world's first all-silicon laser chip. The team foiled silicon's indirect bandgap, which ordinarily prevents lasers from emitting light efficiently, by using stimulated Raman scattering to generate enough optical gain to allow lasing.

By pumping 0.4 microwatt into an on-chip silicon waveguide, the team achieved sufficient gain to initiate 100-nanosecond laser pulses at the 1,669.5-nm wavelength.

"We are reporting Raman lasing in a compact, all-silicon waveguide cavity on a single silicon chip. With devices like this we are demonstrating the true convergence of silicon and optoelectronics," said Mario Paniccia, director of Intel's Photonic Technology Lab.

To beat the indirect-bandgap problem encountered with silicon chips, developers of today's lasers resort to such exotic materials as gallium arsenide or indium phosphide. If an architecture could be devised to sidestep silicon's reluctance to lase, developers could forgo the expense of exotic materials and use cheap silicon instead. "We are being very careful to make sure our silicon photonic devices can be fabricated on standard CMOS lines, so that the future integration of silicon optoelectronics can take advantage of the economies of mass production in our existing facilities," said Paniccia.

To create integrated optical components that are compatible with standard CMOS fabrication facilities, the Intel researchers propose using stimulated Raman scattering in silicon. The technique, which uses vibrations in the material to amplify optical signals, is in wide use today in gallium arsenide-based optical systems.

Stimulated Raman scattering can generate as much as 11-dB optical gain in planar silicon waveguides as small as 1 centimeter by virtue of pulsed light pumping. By fabricating all the necessary components for Raman lasing in a waveguide cavity on a single silicon chip, future silicon optical amplifiers and lasers could eventually be integrated onto standard CMOS chips. Researchers claim the technology could eventually enable a continuous-wave, one-chip silicon laser.